Relay Holding Circuit vs. PLC Holding Program

The automatic holding circuit is often used in various electrical cabinets and is a simple logic circuit. Of course, this simple logic circuit can be built in a large number of PLCs, it is the basis of PLC logic instructions.

What is holding/ self-locking?

Current can flow A to B.

What is relay holding circuit?

Principle of the common relay action:

When the coil is not energized, the normally closedcontact (NC) of the relay can pass current. When the coil is energized, the normally opencontact (NO) of the relay can pass current.

Relay holding circuit

1. Press the button, the current flows from A to C, and the current can also flow from B to C through thenormally open contact of the relay.
2. When the button is reset, the current can still flow from B to C, and the relay maintains the state.

PLC holding program

Let's take Omron PLC as an example.

1. Establish an external I/O contact, I0.00, build an output Q100.00, add a self-locking block, then add disconnection self-holding I0.01, this is a complete self-holding program (start, hold, stop).
2. Simulation, when I0.00 is triggeres, Q100.00 has output. At the same time, Q100.00 is self-locking.
3. When I0.00 is disconnected, the virtual circuit is still connected through Q100.00 self-locking.
4. When I0.01 is triggeres, self-holding becomes invalid.

A summary of relay holding circuit and PLC holdina proaram

1. Compared with PLC, the relay cost is lower, suitable for simple circuit system.
2. The PLC can build a relatively large virtual holding circuit, and can directly output the results during the application process, and which can be used flexibly. And it greatly saves the space of the electrical cabinet.
3. Whether it is a relay holding circuit or a PLC virtual holding circuit, it is now widely used in manufacturing.

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